1. Field of the Invention
The invention relates to photopolymerizable compositions containing an oxonol dye. More particularly, the invention pertains to photopolymerizable compositions comprising an oxonol dye in an admixture of a polymerizable component and a photopolymerization initiator. Such compositions find use as adhesives, coatings, and the like. The compositions cure by exposure to ultraviolet and/or visible radiation, and photobleach to reduce the visible color compared to the pre-cured composition. The photobleaching or disappearance of the visible color of the oxonol dye acts as an indicator of a substantially full cure of the photopolymerizable composition.
2. Description of the Related Art
It is known in the art to produce light sensitive adhesive and coating compositions which adhere to critical surfaces. For example, in the field of medical devices, it is important to inspect catheter interfaces to assure that adjacent surfaces are actually bonded. It is known in the art to incorporate compounds into coating compositions to provide a method for inspection. The prior art describes the incorporation of agents into UV-curable coatings as a means for identifying the presence of a cured film and for insuring that they are properly covered with the coatings. For example, U.S. Pat. No. 6,080,450 describes a visible emitting fluorescing agent to provide a method for the inspection of a UV-cured deposit. Oxonol dyes are well known in the art. U.S. Pat. No. 7,112,616 describes oxonol dyes plus methine, cyanine, and merocyanine dyes for a two-photon absorbing polymerizable composition which is exposed in the non-linear absorption band of the dye. It does not mentioned oxonol dyes having a pyridin-2,6-dione ring nor an 5-oxo-2-isoxazoline ring. The preferred oxonol dyes from this patent have a barbituric acid ring, which has been found to be too fast, such that color changes before cure rather than at or shortly after cure.
The radiation curable composition is composed of a free radical polymerizable component, a free radical photopolymerization initiator, and an oxonol dye. It has now been found that prior to light exposure, the radiation curable composition has a visible color. After exposure, the color is substantially reduced or disappears, and indicates that the composition has been cured. Dye color as measured after exposure for full cure of the radiation curable composition is less than 20% of the original color as measured before exposure. The disappearance of the color occurs at an exposure after full cure and before double that for full cure. The dye color is stable in the photopolymerizable admixture and under non-actinic radiation. For example, if the photopolymerizable admixture is sensitive to UV light and not to visible light, then the dye color changes under UV light and is stable under visible light.
Thus, when the composition is applied to a surface as a coating or between two surfaces as an adhesive, the color remains visible. After being exposed to UV radiation the resonance structure of the dye is destroyed and the dye can no longer resonate thereby decreasing its visible color attribute. The color of the adhesive or coating is substantially reduced and indicates a substantially full cure of the radiation curable composition